This article is only meant as a guide for easier fish and invertebrates to keep, aimed more at beginners; this is far from an exhaustive list of marine fish or invertebrates to keep.
These suggestions are based on my many years of experience setting up literally hundreds of aquariums for clients.
I am also going to add moderate to advanced fish to this list as time permits.

I will add (or maybe even subtract) from this article as time goes on. ANY and ALL suggestions are appreciated and can be emailed to me, as I also respect others experience as well.

I also recommend fish distributed by Quality Marine USA, for their quality and most importantly care. Their fish tend to be a little higher in price, but you are also assured of a quality fish & other reef inhabitants that have received the most humane care possible.

*Notes: The Yellowtail Damsels are generally the most popular damsel fish. These damsels along with Green Chromis are naturally resilient fish and are comparatively peaceful if kept in a shoal in a tank where they feel secure. Be careful with more aggressive Black & White and Domino Damsels, these grow larger and are much more territorial, often killing other damsels in smaller aquariums.
Yellowtail and Green Chromis are excellent starter fish and due well in Reefs and Nano Reefs (although the Green Chromis needs more room IMO, at least a 20 gallon)

*Notes: ALL Pseudochromis are excellent beginner, reef, and Nano reef fish; this includes the Fridmani, Diadema and others. These fish usually are aggressive to other Pseudochromis and Basslets such as Royal Grammas, so I only recommend one in tanks under 40 gallons. With multiple Pseudochromis, please provide ample live rock and sets of three or more do better IMO.

*Notes: Percula as well as similar Ocellaris Clownfish are excellent beginner fish for smaller aquariums as well as larger, Reefs. The Percula Clownfish is a bit more demanding than the Oscellaris or the popular Sebae and Tomato Clown fish.
Perculas as well as Oscellaris seem to do well in pairs. I would be careful in adding pairs of Maroon or Tomato Clownfish unless you know that they are paired male and female.
All anemonefish are born male with active male and dormant female reproductive organs and the female is much larger than the male of the same species, but no color differences differentiate the sexes. Clownfish also have the ability to change sex, where the most dominant male will become a female, and can successfully produce offspring. Clownfish can be bred in an aquarium, and the offspring have been raised successfully for many years.

The Percula Clown or other clownfish do not need an Anemone to survive, but will accept many different Anemones such as the Long Tentacle, Bubble, Saddle, Maroon, and Carpet (be careful with Carpet anemones and other inhabitants that may get caught in them, such as Seahorses).

Please note that if you do decide to add an anemone that your lighting requirements will increase, and that the watts per gallon rule may be a good starting point, it is rather archaic and I highly recommend reading this article for much more about lighting:
“Aquarium Lighting; How it works and more”

ROYAL GRAMMA:*Size: 7.5 cm. (3 in.)
*Family: Grammidae
*Genus: Gramma
*Species: loreto
*Habitat: reefs
*Tank Size: 10 Gallon or larger
*Typical food: Similar to Pseudochromis, Basslets are carnivores but they will often accept frozen foods such as such as mysis shrimp, or frozen prepared foods such as Ocean Nutrition Brine Shrimp Plus; also many dried foods such as plankton or FD Brine Shrimp; and occasionally Pelleted Foods or Flake Foods such as HBH Marine Flake
*Notes; Royal Grammas are territorial to their own kind and often to Pseudochromis as well. I generally recommend only one per tank with plenty of rocks to hide in as they are primarily bottom cave dwellers. Sometimes multiple Basslets will sometimes live together in larger aquariums with lots of rocks to hide in.

*Size: 13 cm. (5 in.)
*Description: Spotted Hawkfish; white body with large red blotches
*Family: Cirrhitidae
*Genus: Cirrhitichthys
*Species: aprinus
*Habitat: reefs
*Tank Size: 10 Gallon or larger
*Typical food: all Hawkfish are carnivores but they will often accept frozen foods such as such as mysis shrimp, or frozen prepared foods such as Ocean Nutrition Brine Shrimp Plus; also many dried foods such as plankton or FD Brine Shrimp; and I have had good results with Flake Foods such as HBH Marine Flake and pelleted foods such as Hikari Marine S Micro Pellets

*Notes; Although all Hawkfish are carnivores, they generally do well in Reefs and Nano Reefs as long as there are no small shrimp. Hawk fish can be aggressive and are best kept one per tank, even in all but the largest aquariums IMO.

- I will also note that Yellow Tangs along with other tangs can also be Detritivores (Althoug it is the Yellow Eye, Chevron and similar tangs that are true Detritivors). What this means is that these fish have the ability to eat detritus and even other fish excrement (poop) and derive nutrition from ingestion of it that other fish cannot, kind of natures recyclers.

*Notes: A great beginner fish for medium to large aquariums, the only note I would make is that they are sensitive to low trace element levels and will get red streaks if your trace elements and alkalinity is not maintained. Yellow Tangs are semi-aggressive fish. They normally get along fine with other semi-aggressive fish close to their own size, but cannot be kept with other yellow tangs (or any other tangs of similar shape/size) - the only exception is if you have lots of them together, like 5 or 6 of them together in a large tank (over 200 IMO). Other possible fish to keep with Yellow Tangs include Hawkfish, hogfish, cardinal fish, angels, clownfish, lionfish, eels, or other different-looking Tangs such as the blue tang. Yellow Tangs are reef-safe, and can be kept with most invertebrates in a reef aquarium.

*Notes: I think these are very beautiful fish and GREAT beginner fish with the possible exception that they seem to be “ich (Cryptocaryon) magnets”, especially when stressed, so quarantine or baths before introduction is advices (please see this article about disease prevention: “Aquarium Disease Prevention”). Regal Blue Tangs are not always tolerant of other similar shaped tangs, although they do well in groups in larger aquariums. I have never experience any problems in my reef tanks with Regal Blue Tang compatibility.

*Notes: This is an aggressive fish. It will compete with all others (mostly angels and some Butterflies) to establish its territory. As for reef compatibility, Koran Angelfish eat soft corals, nibble at Polyped Stony Corals, Zooanthids, and Clams; especially adult Koran Angles (juveniles are less inclined).
Koran Angels will also change coloration as most Pomacanthus angels do. The picture here is of juvenile coloration.

*Size: 15 cm. (6 in.)
*Family: Majidae
*Genus: Stenorhynchus
*Species: seticornis
*Habitat: reefs
*Tank Size: 10 gallon or larger
*Typical food: Opportunistic carnivores, they are not difficult to feed in an established aquarium, especially one that has ample live rock, so specific feeding is not generally necessary. A few suggestions are: Flakes foods high in Spirulina such as HBH Marine Flake, FD foods such as plankton or FD Brine Shrimp, or frozen prepared foods such as Ocean Nutrition Brine Shrimp Plus.

*Notes: Arrow crabs are nocturnal crustaceans, who do all of their scavenging during the nighttime. Arrow Crabs are helpful in aquariums, as they eat fire worms and other aquarium pests that may live in the sand or live rock. The Arrow Crab can be quite territorial, so I only recommend one per tank except for larger aquariums. Generally Arrow Crabs (as with most crabs) are opportunistic feeders and if insufficient food is present they may pick at mushrooms or polyps searching for food.

*Size: 10 cm. (4 in.)
*Genus: Stenopus
*Species: hispidus
*Habitat: reefs
*Tank Size: 10 gallon or larger
*Typical food: Like the Arrow Crab, CBS are opportunistic carnivores, they are not difficult to feed in an established aquarium, especially one that has ample live rock, so specific feeding is not generally necessary. Also similar to Arrow Crabs they will often dine on Polychaete Worms (Bristle Worms, Fireworms). A few suggestions for added foods are: Flakes foods high in Spirulina such as HBH Marine Flake, FD foods such as plankton or FD Brine Shrimp, or frozen prepared foods such as Ocean Nutrition Brine Shrimp Plus.

*Notes: Coral Banded Shrimp look like shrimp however they are not a true shrimp. True Shrimp belong to the infra-order Caridea while Coral Banded Shrimp belong to the infra-order Stenopodidea and are more closely related to lobsters. CBS are best kept singly in an aquarium unless you have a large aquarium with a lot of rock. They are generally nocturnal, although mine have adapted to coming out when food such is added during daylight hours. CBS are generally safe for most reef environments however do to their opportunistic nature, they may prey on small snails, hermit crabs, or shrimp.

*Notes: Turbo Snails are easy to care for however I recommend waiting to add these snails until your aquarium is established so that there is ample algae for them to dine on. Turbo Snails also require adequate calcium levels of 400-450 ppm, SeaChem Reef Calcium Polygluconate is an excellent source of calcium if normal water changes and buffers are not adequate. Also be aware that most Turbo Snails available come from the Gulf of California (Sea of Cortez) where the water are not as warm as other reef inhabitants are used to, so watch your aquarium temperatures and keep them under 80 F. (27 C).

*Size: 41 cm. (16 in.)
*Family: Serranidae
*Genus: Cephalopholis
*Species: miniata
*Habitat: reefs
*Tank Size: 75 gallon or larger (a 125 + is ideal)
*Typical food: Carnivore that prefers whole foods. Suggestions include live feeders that are gut loaded (see this article: “Proper Aquatic Nutrition”) with foods such as Spirulina 20. Other suggestions are FD large Krill/shrimp, or frozen foods such as Ocean Nutrition Prime.
*Notes: Often a shy fish when first introduced, these Groupers readily adapt and are quite hardy. However these fish are NOT reef safe IMO as they eat crustaceans and any smaller fishes they can swallow whole (I have seen them sit outside caves of smaller reef inhabitants waiting for them to come out at feeding time!). I recommend these in larger FOWLR tanks with caves that they can fit in. Good tank mates included any larger fish such as angels, tangs, lionfish, eels, Ect. However I do not recommend another similar Grouper tin the same aquarium.
Although often recommended for aquariums over 125, I have successfully kept many of these Groupers over the years (without stunting or health problems) in 75 gallon aquariums with good filtration, including UV SterilizationVOLITAN LIONFISH (Common Lion Fish, Red or Black):

*Size: 38 cm. (15 in.)
*Family: Scorpaenidae
*Genus: Pterois
*Species: volitans
*Habitat: reefs
*Tank Size: 60 gallon or larger
*Typical food: Carnivore that prefers whole live foods. Suggestions include live feeders that are gut loaded (see this article: “Proper Aquatic Nutrition”) with foods such as Spirulina 20. Lionfish can be a little more difficult to coax to eat other non-live foods however I have has success with FD large shrimp/Krill and similar frozen fare.

*Notes: The Red or Black Volitan is the easiest Lionfish to keep IMO (& experience). The Dwarfs are often more shy and difficult to feed. The Radiata and Antenatta Lions are also simply less hardy in my experience. As with the groupers, Lionfish will consume whatever they can swallow whole and should be kept with fish they cannot fit in their mouth. I would also be careful with some Triggers, which even though they can often be kept together, I have seen Triggers such as the Undulated attack the fins of Lionfish.
As for Reef aquariums, I have on occasion kept them in reefs devoid of shrimps or other similar prey and they have done fine. I have heard of Lionfish getting stung by large carpet anemones when resting, however I have never witnessed this.

*Size: 25 cm. (10 in.)
*Family: Balistidae
*Genus: Rhinecanthus
*Species: aculeatus
*Habitat: Fish only (not compatible delicate corals, etc.)
*Tank Size: 60 gallon or larger
*Typical food: Carnivore, although not a fussy carnivore, rather an opportunistic carnivore that usually will eat most meaty foods offered. Although not a necessity as in Clown Triggers, I highly suggest Urchin in these Triggers diet, this can be found in Ocean Nutrition Trigger Diet. Other foods include Ocean Nutrition Prime, Large Krill/ Shrimp, and FD plankton/ Small Shrimp
*Notes: The Humu-Humu/Picasso from Hawaii and the similar Rectangulatus Trigger also form Hawaii are two of the easiest Triggerfish to keep and among the least aggressive, especially when compared to the Undulated or Pink Tail Triggers. That said they still should be kept with larger fish that they cannot threaten such as Lionfish, Large Angels, Tangs, ect. This Genus of Triggers are generally compatible in larger aquariums with others of the same Genus unlike Undulated or Pink Tails. These Triggers are also hardier and less expensive to purchase than the beautiful but more delicate Clown Trigger (which must have urchin in their diet).

Notes: These are two of the more beautiful marine fish you can keep IMO and although I would not classify them as a true beginner fish, they are just one step up in care. I have found these fish are only difficult when the tank environment is not at its best and/or these angels are not fed a variety of foods, especially algae such as Spirulina or Caulerpa.
Dwarf Angels are somewhat Reef Compatible, however they may pick at delicate corals, so caution should be exercised in placement in reef tanks. Most Dwarf angels are also not very tolerant of others of the same species or genus, especially in smaller aquariums.

*Size: 46 cm. (18 in.)
*Family: Acanthuridae
*Genus: Naso
*Species: lituratus
*Habitat: reefs
*Tank Size: 100 gallon or larger
*Typical food: Herbivore, although Naso Tangs will eat meaty foods as well such as Brine Shrimp, chopped squid, and Mysis Shrimp. However Naso tangs must be able to graze on a regular basis (if not these can be more difficult fish to keep and they will waste away). Using a clip or rubber band attached to a rock are popular ways to feed Naso Tangs foods such as dried algae, spinach or Romaine Lettuce, however I only recommend Romaine lettuce in a pinch as this is mostly cellulose and fed long term will lead to poor health in my experience. Other foods that are excellent additions to their diet include prepared frozen foods such as Ocean Nutrition; Spirulina Formula, Ocean Nutrition Formula II or Brine Shrimp Plus and flake foods such as Spirulina 20.

*Notes: The Naso Tang is usually imported from Hawaii, however these fish are common to the entire Indo-Pacific Region with some beautiful specimens coming from Australia.
The Naso Tang from Hawaii is dark gray with a blue stripe following along the dorsal fin and an orange stripe in the anal fin while a Juvenile. When matured, the body takes on a reddish-brown tone and the juvenile striping is supplemented with additional color. The tail takes on a lyre shape with a yellow vertical bar towards the back.
I have generally found Naso Tangs a little more of a challenge to keep, however with a good and varied diet, lots of room, a healthy environment which in my opinion includes a UV Sterilizer for disease control and more importantly for Redox Potential, these fish can be kept without too many problems.
These Tangs need lots of room to swim and are compatible with most fish except others of the same species (except in large groups). Naso Tangs are generally safe for most reef inhabitants such as Corals.

*Size: 46 cm. (18 in.)
*Family: Actiniidae
*Genus: Macrodactyla
*Species: doreensis
*Habitat: reefs
*Tank Size: 40 gallon or larger
*Mature Size; Up to 20 inches
*Typical food: The LT Anemone is photosynthetic which is performed by zooxanthellae.
As well this anemone is also a Carnivore and should include fish, brine shrimp, crustaceans and mussels, zooplankton, phytoplankton, and frozen foods such as Ocean Nutrition Prime, Squid or similar.

One of the most popular anemones along with Bubble Tip (BTA) for reef aquariums and hosting some clownfish.
Long Tentacle Anemones generally hide in the rubble or sand with just its tentacles being visible.

Long Tentacle Anemones require:
*Medium lighting is required as this is an photosynthetic animal. See this article: "Aquarium Lighting"),
*Medium and variable circulation (usually provided by power heads, propeller pumps)
*Plenty of coral rubble and live rock to move around in and high points to get closer to lights if necessary.

These can also be semi-aggressive anemones towards other tank mates such as sps corals.
Generally stinging of sps or other corals is not a problem as these anemones rarely "stay put". When "parked" next to an sps coral they may sting it, but usually the time spent in one location is not enough to kill an sps coral. However I would suggest the ratio of LT Anemones to sps corals be very low; as an example only one LT Anemone in a 60 gallon reef tank that also has plenty of corals.

*Size: 35 cm. (14 in.)
*Family: Labridae
*Genus: Coris
*Species: gaimard
*Habitat: Fish only (not compatible delicate corals, etc.)
*Tank Size: 75 gallon or larger
*Typical food: Carnivore; I recommend vitamin enriched Mysis Shrimp, Brine Shrimp (such as Ocean Nutrition Brine Shrimp Plus or similar), also since these fish eat shelled mollusks in the wild including hermit crabs, urchins, and crabs in the wild, I would recommend providing open clams for them to dine on. Occasionally Red Coris Wrasse will accept Flake Foods such as HBH Marine Flake are sometimes accepted however these should never be used as the sole diet for Red Coris Wrasse.
Notes: These can be difficult fish to adapt upon arrival to a new aquarium, so extra care in handling and dripping water into the shipping bag should be given. Also, Red Coris Wrasse also needs a FINE sand bed of at least 2 inches (5 cm) in which to bury themselves and hide (which is their normal behavior when frightened or even resting). I only recommend these fish for more advanced aquarists however in the right conditions these fish can be kept relatively easily once they have adapted to the aquarium. I also hve found these fish more susceptible to diseases such as Cryptocaryon, so extra care should be given to prevent this form introduction, low stress environment, healthy Redox, to UV Sterilization.

*Size: 10 cm. (4 in.)
*Genus: Pseudocolochirus
*Species: axiologus (Indonesia) & iolaceus (Australia)
*Habitat: Reef; NO aggressive fish that would add stress possibly causing the rare release of toxins into the water (or invertebrates such as a carpet anemone)
*Typical food: Filter Feeder.
I have had reasonable success (with Sea Apples living well over a year by making pea green mixture of Spirulina 20 Fish Food Flake and water not too soupy), then feeding with a syringe near the Sea Apple (which should be in a high flow area of the aquarium)

Sea Apples (which are a type of Sea Cucumber) are often sold as a beginner invertebrate, while in reality they require more work just to keep fed (which can be difficult to know for sure too).
While strong lighting is not a factor from my experience, very good water conditions ARE a factor.

These are also animals that are best in an aquarium where other inhabitants leave them alone. Sea Apples have a variety of defenses that are generally utilized prior to a general release of their toxic chemicals which can harm fish and other inhabitants in a closed aquarium. While I have not had a known "die-off" from a toxic chemical release, I have heard form those that have had this happen.
Should this happen, generally water changes and a good amount of carbon and products such as Purigen should take care of the problem.

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